Introduce an optional Predicate<String> targetAttributeFilter to control how grpc.target is recorded in OpenTelemetry client metrics.

When a filter is provided, targets rejected by the predicate are normalized to "other" to reduce grpc.target metric cardinality, while accepted targets are recorded as-is. If no filter is set, existing behavior is preserved.

This change adds a new Builder API on GrpcOpenTelemetry to allow applications to configure the filter. Tests verify both the Builder
wiring and the target normalization behavior.

This is an optional API; annotation (e.g., experimental) can be added
per maintainer guidance.

Refs #12322
Related: gRFC A109 – Target Attribute Filter for OpenTelemetry Metrics
grpc/proposal#528